ABSTRACT
Potato (Solanum tuberosum L.) is an economically-important food crop cultivated and consumed all over the world. In total food production, potato ranks fourth after wheat, maize and rice (Heling 1998). Potato varieties with higher yield, better agronomic qualities and resistance to diseases are of immense importance for increased production (Naik and Sarkar 2000). However, the process of varietal improvement through conventional breeding is time consuming as well as complicated and laborious due to tetrasomic segregation pattern and incomplete fertility in many tetraploid cultivars. Many good cultivars are susceptible to virus infection, fungal and bacterial diseases such as late blight, ringrot, black leg, bacterial wilt, etc., leading to major yield losses. Among viruses, Potato Virus Y (PVY), Potato Virus X (PVX) and Potato Leaf Roll Virus (PLRV) are the major viral pathogens, while Potato Virus S, Potato Virus
A and Potato Virus V comprise the other notable ones (Khurana 1992). Potyviruses (PVY, PVA, PW ) cause major damage to potato crop and 30 to 40% yield loss is quite common (Rykbost et al., 1999). Infection of tobacco with PVY strains indigenous to southeastern United States resulted in a yield reduction ranging from 10 to 100% (Gooding and Tolin 1973). A synergistic effect involving a dual infection of PVY and PVX can cause serious damage to the crop in the field (Pruss et al., 1997).
